This invention relates generally to video processing and more particularly to sub-picture scaling and blending.
Displaying typical television/video source data on computers is known. Such television video includes television broadcasts signals, cable television signals, satellite television signals, VCR signals and DVD signals. To display such traditional television signals on a computer display, the video signals must be processed according to traditional computer display processing.
For example, traditional television signals are interlaced such that one field of video data includes only an odd, or even, line of video data, while the next field includes the next even, or odd, line. Generally, graphic signals for computer displays are non-interlaced signals, as such, graphic signals include both the odd and even lines in the same frame. In addition, a television""s display size is typically different than that of a computer display. For example, a standard television set is usually 720 pixelsxc3x97480 pixels, 720 pixelsxc3x97525 pixels, or letterbox, while a typical computer display is 640 pixelsxc3x97480 pixels. As such, the traditional television video signals must be scaled, deinterlaced, and converted to a graphics format before they can be displayed on a computer monitor.
There are a variety of ways in which video data may be scaled. For example, when video data is to be upscaled (i.e., the target display is larger than the source display), pixel information may be repeated in several pixel locations to fill in the extra pixels of the upscaled display. Alternatively, pixel information may be blended within an area to fill in additional pixel locations that result from upscaling. For down-scaling, the pixel information at a given pixel location is a result of merging pixel information of surrounding pixel locations of the source display. The merging may be a blending, averaging, selecting one of the pixel as a representative pixel, or combination thereof.
When a DVD video source is to be displayed on a computer screen, wherein the DVD data includes a video data stream and a sub-picture data stream, the video data and the subpicture data are decoded and stored in a frame buffer. In a typical computer video processing circuit, the DVD video data and the DVD subpicture data (which includes buttons for controlling DVD applications, selecting different chapters, or titles within the DVD video, etc.) are decoded, stored, and blended together to produce pixel information. The pixel information is then stored in a frame buffer. Prior to displaying the pixel information on a computer monitor, it is scaled to fit the allocated display area of the computer monitor.
The most common blending technique for DVD video data and subpicture data does not includes blending of the data, but produces blended visual affects by alternating between the video data and the subpicture data. In other words, holes are provided within the DVD subpicture data and filled with the DVD video data, or vice versa. The more holes there are, the more the DVD video data is visible. While this method produces an illusion of blending without the multiple read-write operations of alpha blending (discussed below), it does so with reduced video quality when compared to alpha blending.
While alpha blending would produce a higher quality picture, it does so at a cost that is prohibitive to commercial use. In order to alpha blend the DVD video data and the DVD subpicture data, the DVD subpicture data needs to be completely decoded. As is known, the DVD subpicture data is encoded based on run length encoding, which includes a repeating pattern and how often it is repeated. Such encoding, however, does not provide an indication as to the beginning of a line within a frame, or field, of data. Thus, the DVD subpicture needs to be completely decoded and stored in a separate frame buffer from the DVD video data. Once the decoded subpicture data is obtained, it can be blended with the video data and re-written into the frame buffer. This approach requires a read-write-read operation and a substantial amount of additional memory. The read-write-read operation for commercial processors is too process intensive to allow alpha blending to be a viable commercial solution for DVD video and subpicture data blending. The additional memory required also limits the commercial viability of the alpha blending.
Therefore, it is desirable to develop a method and apparatus that blends DVD video data and DVD subpicture data without substantially increasing memory and processing requirements for video processing circuits.